The South Collector drains water from the left bank of the upper Arve valley. It obtains the 44km² of water from watersheds located between Argentière and Le Tour, above an elevation of 2000m. At its origin, it is extended upstream by a pipe collecting the contributions of five water intakes installed on streams coming from the Lognan glacier between the elevations of 2069m and 2062m.

The South Collector itself consists of a 5.7m² tunnel (2.6m in diameter) left for rough excavation over approximately three quarters of its length, with the exception of the completely lined apron.

This tunnel, 8.55km long and equipped for a flow of 12m³/sec, begins on the left bank of the Argentière glacier at a height of 2062m. It crosses the Argentière glacier from below, collecting the waters of the sub-glacial stream on the way. Once crossed the glacier, it heads towards a point located east of the Balme pass where it bends up and over towards the west so as to remain substantially parallel to the Franco-Swiss border.

Finally, it emerges at an elevation of 1994m at a place called Belleplace, on the right bank of the Eau-Noire. The waters arriving via this tunnels are led towards the Vallorcine power station situated 860m lover down where they can be turbined directly or siphoned into the Emosson reservoir by using the reinforced shaft located on the opposite bank.

The main structures encountered from upstream to downstream are: the Argentière and Le Tour catchments, the Belleplace facilities (underwater siphon, head valves, surge well), the reinforced shaft.